The present invention relates to a composition comprising at least one ionomeric polyester resin and at least one organoclay. The invention also relates to a method for improving modulus properties of a resinous composition containing at least one polyester resin and at least one organoclay.
Organoclays typically consist of particles comprised of several layers of alumino-silicate plates held together by electrostatic interactions with organic moieties containing metal cations or alkyl ammonium ions intercalated between the plates. Such clays have been used as fillers in resinous compositions. In certain cases they may increase properties such as heat resistance, and/or mechanical strength, or they may beneficially decrease properties such as electrical conductivity or permeability to gases such as oxygen or water vapor.
The benefit of organoclays over other mineral fillers in resinous compositions is obtained when the alumino-silicate plates comprising the clay are separated from one another and dispersed in the polymer matrix. Since these plates have a very high aspect ratio, they may provide property enhancement such as reinforcement and improvement in modulus compared to traditional mineral fillers on a per weight of total inorganic content. In order to separate the layers of the clay and obtain maximum reinforcement in a resinous composition, it is typically necessary that polymer adsorb between the layers of the clay causing exfoliation (separation) of the layers. Typically, hydrophilic polymers such as polyamides or water-soluble polymers have been used in compositions with organoclays since they may have an affinity for the clay surface promoting exfoliation. It has been found, however, that intimately mixing typically hydrophobic polyester resins and organoclays does not allow for full exfoliation of the clay. Thus properties of the compositions such as modulus may be only marginally better than those properties obtained when traditional fillers are used in typical polyester resins. There is a need to prepare compositions of normally hydrophobic polyester resins with organoclay fillers which achieve optimum beneficial property improvement.
PCT Patent Application WO 99/32403 suggests the preparation of an expanded organoclay using a sulfonated polyester as an expanding agent. Following the expansion step, the expanded organoclay is combined in a separate step with a non-ionomeric polyester resin to form a composition with up to 30 weight % expanded organoclay, the clay containing 20 to 80 weight % expanding agent.
Japanese Kokai Patent Application No. Hei 10-324810 discloses a resin composite material characterized in that organically modified clay is dispersed in an ionomeric polyolefin resin. However, the use of ionomeric polyesters is not suggested.
The present inventors have now discovered that an organoclay may be effectively dispersed in a polyester resin-containing composition when an ionomeric polyester resin is present. Therefore, in one embodiment the present invention is a composition comprising at least one ionomeric polyester resin and at least one organoclay.
In another embodiment the present invention is a method for improving the modulus properties of a resinous composition comprising at least one organoclay, the method comprising the steps of combining the resinous composition with at least one ionomeric polyester, and intimately mixing the composition.